The principal objectives of this proposal are to gain a clearer understanding of local metabolic regulation of blood flow, with particular emphasis on the role played by adenosine and to determine the factors involved in the formation and release of adenosine. The release of adenosine from the heart of the unanesthetized dog will be measured under different physiological and pathophysiological states such as graded exercise, excitement, eating, hypertension and coronary artery constriction and correlated with changes in coronary blood flow, cardiac output, arterial blood pressure and heart rate. Also, the rapidity of adenosine formation in ischemic hearts, the activity of 5'-nucleotidase in epicardium and endocardium and the movement of adenosine across endothelial cells will be studied. In brain, the magnitude of adenosine formation and release will be examined in the unanesthetized animal subjected to hypoxia, hypo and hypercapnia, hypotension, convulsions and activation of the somato-sensory cortex. Also, the effect of photic stimuli on the relationship between blood flow of the visual cortex and adenosine formation will be studied in the unanesthetized animal. In isolated sympathetic ganglia, the contribution of pre and post synaptic activation of adenosine release will be assessed. In skeletal muscle the regulation of 5'-nucleotidase activity will be studied in red and white muscle before and after cross innervation and induction of 5'-nucleotidase synthesis will be studied in pure cell cultures of skeletal muscle. Autoregulation of liver blood flow will be examined with respect to O2 supply and vasoactive metabolite release. Finally, dispersed cell preparations from heart, liver and fat (fat ghost cells) will be used to elucidate the factors responsible for regulation of the membrane-bound enzyme, 5'-nucleotidase. In addition to providing new information on the regulation of adenosine release, these studies will set the stage for evaluating the role of adenosine in blood flow regulation in human beings.